OH! and I put a bit of spray paint on the fiberglass/grout background. It's starting to look almost real! Now I need to seal the caves with epoxy. I kinda want to get ahold of some of my substrate (whatever it turns out to be in the end) before I do this though, so I can blast some substrate at the half-dry eboxy and have it stick there... so I can get a bit of ontinuity between the substrate and the caves.... but then again, I might just be being a bit anal...